A horizontal rotary hook providing an easy replacement of a bobbin has conventionally been used in sewing machines. The horizontal rotary hook comprises an outer rotating hook formed with a lace and an inner bobbin case holder which accommodates a bobbin and is held so as to be rotatable relative to the lace face. The rotating hook is adapted to be rotated in a predetermined direction by a sewing machine motor or the like.
The bobbin case holder is made of a synthetic resin so that a reduction is achieved in the weight and production cost thereof. Furthermore, the rotating hook has also been made of a synthetic resin recently. In this case, a beak is provided on an outer peripheral wall of the rotating hook for seizing a loop of bobbin thread. However, when the beak is formed integrally on the rotating hook, the structure of a forming die used for forming the rotating hook is complicated. Furthermore, the beak necessitates a higher strength than the other part of the rotating hook. In view of these problems, a beak member provided with a beak has been proposed to be formed separately from the rotating hook and mounted on the rotating hook. For example, JP-U-S60-149388 discloses a horizontal rotary hook in which a beak is made of a metal and mounted on an inner peripheral surface of an outer peripheral wall of the hook so as to be laid on the inner peripheral surface.
However, a thickness of a part of the rotating hook on which the beak member is laid is increased when the beak member is mounted inside the outer peripheral wall of the rotating hook. Consequently, the size of the horizontal rotary hook is increased.
In order that the increase in the size of the overall horizontal rotary hook may be limited, the beak member is suggested to be disposed in an opening formed by cutting out the outer peripheral wall of the horizontal rotary hook and mounted to the bottom of the rotating hook by screws so as to joined to the rotating hook. However, when the beak member is simply mounted to the bottom of the rotating hook made of the synthetic resin, a sewing thread is entangled in a space defined between the inner rotating hook and the beak member. Upon occurrence of such thread entanglement, the beak member is instantaneously subjected to a large external stress traveling outward. As a result, the beak member is deformed or a part of the beak member mounted to the outer rotating hook is damaged.